1. Field of the Invention
The invention relates generally to signal amplification systems, and more particularly to systems and methods for driving a pair of high-voltage transistors in a pulse width modulated audio amplification system.
2. Related Art
Pulse Width Modulation (PWM) or Class D signal amplification technology has existed for a number of years. PWM technology has become more popular with the proliferation of Switched Mode Power Supplies (SMPS). Since this technology emerged, there has been an increased interest in applying PWM techniques in signal amplification applications as a result of the significant efficiency improvement that can be realized through the use of Class D power output topology instead of the legacy (linear Class AB) power output topology.
Early attempts to develop signal amplification applications utilized the same approach to amplification that was being used in the early SMPS. More particularly, these attempts utilized analog modulation schemes that resulted in very low performance applications. These applications were very complex and costly to implement. Consequently, these solutions were not widely accepted. Class D technology was therefore unable to displace legacy Class AB amplifiers in mainstream amplifier applications.
Recently, digital PWM modulation schemes have surfaced. These schemes use Sigma-Delta modulation techniques to generate the PWM signals used in the newer digital Class D implementations. These digital PWM schemes, however, did little to offset the major barriers to integration of PWM modulators into the total amplifier solution. Class D technology has therefore continued to be unable to displace legacy Class AB amplifiers in mainstream applications.
There are a number of problems with existing digital PWM modulation schemes. One of the problems is that the audio system has to drive a pair of high-voltage field effect transistors (FETs) at the output of the system. Thus, is typically necessary to provide a high-voltage driver circuit to drive the FETs. Generally speaking, it is more difficult to design a high-voltage driver circuit than a low-voltage driver circuit, and it is more complicated and expensive to manufacture the high-voltage circuit. Another problem with existing schemes is that they do not to provide significant control over the individual FETs in terms of controlling delays in the corresponding signals and enabling shutdown of the FETs.